First commit on my server, yey!

Packages/com.jovian.savesystem/Runtime/Slots/SaveSessionInfo.cs

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+using System;
+
+namespace Jovian.SaveSystem {
+    /// <summary>
+    /// Describes a save session (a new game playthrough).
+    /// </summary>
+    [Serializable]
+    public sealed class SaveSessionInfo {
+        public string sessionId;
+        public long creationDateUtc;
+        public long lastSaveDateUtc;
+
+        public DateTime CreationDateTime => DateTimeOffset.FromUnixTimeMilliseconds(creationDateUtc).UtcDateTime;
+        public DateTime LastSaveDateTime => DateTimeOffset.FromUnixTimeMilliseconds(lastSaveDateUtc).UtcDateTime;
+    }
+}

Packages/com.jovian.savesystem/Runtime/Slots/SaveSessionInfo.cs.meta

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+fileFormatVersion: 2
+guid: f03201423cd9f364c85bc6ce44386fbd

Packages/com.jovian.savesystem/Runtime/Slots/SaveSlotInfo.cs

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+using System;
+
+namespace Jovian.SaveSystem {
+    /// <summary>
+    /// Describes a single save slot within a session.
+    /// </summary>
+    [Serializable]
+    public sealed class SaveSlotInfo {
+        public string sessionId;
+        public SaveSlotType slotType;
+        public int slotNumber;
+        public string filePath;
+        public long timestampUtc;
+        public int saveVersion;
+
+        public string DisplayLabel =>
+            slotType switch {
+                SaveSlotType.Manual => $"Manual Save {slotNumber}",
+                SaveSlotType.Auto => $"Auto Save {slotNumber}",
+                SaveSlotType.Quick => "Quick Save",
+                _ => "Unknown"
+            };
+
+        public DateTime TimestampDateTime => DateTimeOffset.FromUnixTimeMilliseconds(timestampUtc).UtcDateTime;
+    }
+}

Packages/com.jovian.savesystem/Runtime/Slots/SaveSlotInfo.cs.meta

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+fileFormatVersion: 2
+guid: c10256ba563528a4c9d92d158c6c009c

Packages/com.jovian.savesystem/Runtime/Slots/SaveSlotManager.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Newtonsoft.Json;
+
+namespace Jovian.SaveSystem {
+    /// <summary>
+    /// Manages save slot allocation, session tracking, and auto-save rotation.
+    /// Maintains a persistent index file that tracks all sessions and their slots.
+    /// </summary>
+    public sealed class SaveSlotManager : ISaveSlotManager {
+        private const string IndexFileName = "index.json";
+        private const string ManualPrefix = "manual_";
+        private const string AutoPrefix = "auto_";
+        private const string QuickFileName = "quick.sav";
+        private const string SaveExtension = ".sav";
+
+        private readonly ISaveStorage storage;
+        private readonly int maxAutoSaves;
+        private SaveIndex index;
+
+        public SaveSlotManager(ISaveStorage storage, SaveSystemSettings settings) {
+            this.storage = storage;
+            maxAutoSaves = settings.maxAutoSavesPerSession;
+            LoadIndex();
+        }
+
+        public string CreateSession() {
+            string sessionId = Guid.NewGuid().ToString("N");
+            SaveSessionInfo session = new SaveSessionInfo {
+                sessionId = sessionId,
+                creationDateUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+                lastSaveDateUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
+            };
+
+            index.sessions.Add(session);
+            storage.CreateDirectory(sessionId);
+            PersistIndex();
+            return sessionId;
+        }
+
+        public SaveSlotInfo AllocateManualSlot(string sessionId) {
+            List<SaveSlotInfo> sessionSlots = GetOrCreateSessionSlots(sessionId);
+            int nextNumber = sessionSlots
+                .Where(s => s.slotType == SaveSlotType.Manual)
+                .Select(s => s.slotNumber)
+                .DefaultIfEmpty(0)
+                .Max() + 1;
+
+            SaveSlotInfo slot = new SaveSlotInfo {
+                sessionId = sessionId,
+                slotType = SaveSlotType.Manual,
+                slotNumber = nextNumber,
+                filePath = $"{sessionId}/{ManualPrefix}{nextNumber:D3}{SaveExtension}",
+                timestampUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
+            };
+
+            index.slots.Add(slot);
+            return slot;
+        }
+
+        public SaveSlotInfo AllocateAutoSlot(string sessionId) {
+            List<SaveSlotInfo> sessionSlots = GetOrCreateSessionSlots(sessionId);
+            List<SaveSlotInfo> autoSlots = sessionSlots
+                .Where(s => s.slotType == SaveSlotType.Auto)
+                .OrderBy(s => s.slotNumber)
+                .ToList();
+
+            if(autoSlots.Count >= maxAutoSaves) {
+                // Rotate: reuse the oldest slot
+                var oldest = autoSlots.OrderBy(s => s.timestampUtc).First();
+                oldest.timestampUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
+                return oldest;
+            }
+
+            int nextNumber = autoSlots.Count + 1;
+            SaveSlotInfo slot = new SaveSlotInfo {
+                sessionId = sessionId,
+                slotType = SaveSlotType.Auto,
+                slotNumber = nextNumber,
+                filePath = $"{sessionId}/{AutoPrefix}{nextNumber:D3}{SaveExtension}",
+                timestampUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
+            };
+
+            index.slots.Add(slot);
+            return slot;
+        }
+
+        public SaveSlotInfo AllocateQuickSlot(string sessionId) {
+            List<SaveSlotInfo> sessionSlots = GetOrCreateSessionSlots(sessionId);
+            SaveSlotInfo existingQuick = sessionSlots.FirstOrDefault(s => s.slotType == SaveSlotType.Quick);
+
+            if(existingQuick != null) {
+                existingQuick.timestampUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
+                return existingQuick;
+            }
+
+            SaveSlotInfo slot = new SaveSlotInfo {
+                sessionId = sessionId,
+                slotType = SaveSlotType.Quick,
+                slotNumber = 1,
+                filePath = $"{sessionId}/{QuickFileName}",
+                timestampUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
+            };
+
+            index.slots.Add(slot);
+            return slot;
+        }
+
+        public IReadOnlyList<SaveSlotInfo> GetSlots(string sessionId) {
+            return index.slots
+                .Where(s => s.sessionId == sessionId)
+                .OrderByDescending(s => s.timestampUtc)
+                .ToList();
+        }
+
+        public IReadOnlyList<SaveSessionInfo> GetAllSessions() {
+            return index.sessions
+                .OrderByDescending(s => s.lastSaveDateUtc)
+                .ToList();
+        }
+
+        public bool HasAnySaves() {
+            return index.slots.Count > 0;
+        }
+
+        public void DeleteSlot(SaveSlotInfo slot) {
+            storage.Delete(slot.filePath);
+            index.slots.RemoveAll(s => s.filePath == slot.filePath);
+            PersistIndex();
+        }
+
+        public void DeleteSession(string sessionId) {
+            List<SaveSlotInfo> slotsToDelete = index.slots
+                .Where(s => s.sessionId == sessionId)
+                .ToList();
+
+            foreach(SaveSlotInfo slot in slotsToDelete) {
+                storage.Delete(slot.filePath);
+            }
+
+            index.slots.RemoveAll(s => s.sessionId == sessionId);
+            index.sessions.RemoveAll(s => s.sessionId == sessionId);
+            PersistIndex();
+        }
+
+        public void UpdateSlotMetadata(SaveSlotInfo slot, long timestampUtc, int saveVersion) {
+            slot.timestampUtc = timestampUtc;
+            slot.saveVersion = saveVersion;
+
+            SaveSessionInfo session = index.sessions.FirstOrDefault(s => s.sessionId == slot.sessionId);
+            if(session != null) {
+                session.lastSaveDateUtc = timestampUtc;
+            }
+        }
+
+        public void PersistIndex() {
+            string json = JsonConvert.SerializeObject(index, Formatting.Indented);
+            byte[] bytes = Encoding.UTF8.GetBytes(json);
+            storage.Write(IndexFileName, bytes);
+        }
+
+        private void LoadIndex() {
+            if(!storage.Exists(IndexFileName)) {
+                index = new SaveIndex();
+                return;
+            }
+
+            try {
+                byte[] bytes = storage.Read(IndexFileName);
+                string json = Encoding.UTF8.GetString(bytes);
+                index = JsonConvert.DeserializeObject<SaveIndex>(json) ?? new SaveIndex();
+            } catch(Exception) {
+                index = new SaveIndex();
+            }
+        }
+
+        private List<SaveSlotInfo> GetOrCreateSessionSlots(string sessionId) {
+            if(!index.sessions.Any(s => s.sessionId == sessionId)) {
+                SaveSessionInfo session = new SaveSessionInfo {
+                    sessionId = sessionId,
+                    creationDateUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds(),
+                    lastSaveDateUtc = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()
+                };
+                index.sessions.Add(session);
+                storage.CreateDirectory(sessionId);
+            }
+
+            return index.slots.Where(s => s.sessionId == sessionId).ToList();
+        }
+
+        /// <summary>
+        /// Internal index structure persisted to disk.
+        /// </summary>
+        [Serializable]
+        private sealed class SaveIndex {
+            public List<SaveSessionInfo> sessions = new List<SaveSessionInfo>();
+            public List<SaveSlotInfo> slots = new List<SaveSlotInfo>();
+        }
+    }
+}

Packages/com.jovian.savesystem/Runtime/Slots/SaveSlotManager.cs.meta

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+fileFormatVersion: 2
+guid: 9498521d42a48944ba38a961e8e82459